Over 26 million people in the U.S. have chronic kidney diseases, most commonly from diabetic glomerular injury. However, progression to end stage is more tightly coupled to proximal tubule disappearance (tubular atrophy), which is caused by apoptosis. In the previous funding period we determined that intracellular accumulation of a non-esterified fatty acid (NEFA) metabolite, long-chain acyl-coenzyme A (LC-CoA), stimulates tubular atrophy by a mechanism that involves inhibition of NHE1 Na+/H+ exchanger-dependent cell survival. Excess LC-CoAs are stored as cytoplasmic lipid droplets to shield cells from lipotoxicity, though this NEFA buffering capacity is limited in the proximal tubule. Multiple factors converge to cause NEFA accumulation in diabetic nephropathy, but most notably reabsorption of filtered albumin bound to NEFA. We hypothesize that luminal NEFA uptake by fatty acid transporter-2 (FATP2) causes proximal tubule lipoapoptosis, which contributes to tubular atrophy and progression of diabetic nephropathy. The hypothesis will be pursued with the following specific aims: (1) To determine whether FATP2 is the major transporter for luminal proximal tubule NEFA uptake, fluorescently labeled NEFA uptake will be measured in isolated perfused proximal tubules from FATP2-deficient mice, and apoptosis will be assayed in cultured proximal tubule cells treated with shRNAs directed against FATP2; (2) To determine the pathophysiological relevance of FATP2- mediated NEFA internalization in diabetic nephropathy 13C-labeled NEFA uptake will be assayed in vivo in eNOS???db/db mice prone to diabetic nephropathy, and the effects of insulin on FATP2-dependent NEFA uptake in proximal tubule cells will be measured; (3) Genetic and pharmacologic tools will be employed to test whether proximal tubule NEFA uptake regulates diabetic nephropathy progression in eNOS???db/db mice. Upon completion of these experiments we are hopeful that FATP2 will emerge as a druggable target for the treatment of diabetic nephropathy.